The present invention relates to a CAD/CAM apparatus and a machining apparatus in consideration of force information, and more particularly to a CAD/CAM apparatus and a machining apparatus in which path data having position and force information or energy as attributes are calculated in accordance with a predetermined algorithm on the basis of shape information, machining information and machined surface information of a workpiece to thereby perform force control in addition to positional control so that high quality and stable shape precision and surface roughness may be obtained.
FIG. 9 shows a conventional CAM system. A shape of a workpiece 3 is modeled by a CAD 1. At this time, in order to produce a machining program, the operation of producing surface information (recognizing the portions surrounded by lines as surfaces) or producing coupling information of surfaces is performed together by the CAM. Then, on the basis of the shape modeling data, parameters such as a machining starting point, an approach velocity, a pitch amount, a removal allowance, a tool to be used or the like (hereinafter referred to as machining information) are supplied to a tool path calculation section 5 to perform the calculation and the compilation of the path. These operations are performed for every machining step (rough machining, intermediate machining and finishing). It is however possible to compile a plurality of machining steps as continuous data. Then, an NC machining program (G-code, M-code) is automatically produced in a program producing section 7 in accordance with the path data calculated in the tool path calculation section 5. Since this program is output as a text file, it is possible to compile it by use of an editor. Subsequently, in accordance with the NC machining program produced in the program producing section 7, the establishment of target values for the positional and velocity control of the tool or the replacement of the tools are performed in a position/motion planning section 9, and the workpiece 3 is automatically machined in a positional control section 11. Since the conventional CAM system handles only positional (and velocity) information, the system is suitable for cutting work (or grinding work) requiring high shape precision. As a matter of fact, almost all CAM systems are used for cutting type machining.
However, it is necessary to identify the surface roughness with a target value when performing grinding work (or cutting work for the purpose of finishing) as shown in FIG. 10. Accordingly, force control is needed in addition to the positional control. Accordingly, the conventional CAM system which does not provide for force control, is not suitable for the grinding type machining, and it is difficult to automatically perform such an operation. Also, this becomes one of the factors that makes it difficult to automatically perform an operation such as grinding machining.
Furthermore, even in the case where force control is handled by the CAM system and it is applied to the actual grinding robot to perform the grinding work, in order to realize a high quality grinding surface, the system suffers from the following defects.
A conventional grinding robot is shown in FIG. 11. In FIG. 11, a grinding unit 31 is a rotary type grinding machine such as a PVA (polyvinyl alcohol) grinding stone or a buff grinding unit. A buff 35 is driven by drivers 33a and 33b. The workpiece 3 is held by a robot 39 and is depressed against the buff 35 by a force f(t) in a direction x to thereby grind a predetermined surface. The buff 35 is moved at a velocity V(t) in a direction y (where the velocity in the tangential direction of the buff 35 at a tangential point is defined at V(t)). In this case, t is the grinding time when the workpiece 3 is depressed to the buff 35. In this control, the force f.sub.mx (t) (not shown) in the direction x which is given to the workpiece 3 by the robot 39 is adjusted so that the force f(t) becomes a predetermined value.
However, in the conventional control, even in the case where clogging occurs in, for example, the buff 35 and the frictional force F(t) (which is the frictional force in the tangential direction at the tangential point of the outer circumference of the grinding unit 31) between the buff 35 and the workpiece 3 is reduced, the constant force f(t) is simply applied for a predetermined period of time. As a result, there is a concern that the grinding work is not sufficiently performed. In this control, ideally, it is necessary to increase the force f(t) corresponding to the decrement of the frictional force F(t) or to elongate the grinding time t. Namely, since the frictional coefficient between the buff 35 and the workpiece 3 is delicately changed in accordance with various conditions, it is not possible to perform stable grinding work in the control of the force f.sub.mx (t) in the direction x supervising the force f(t) in the direction x. On the other hand, the essence of the grinding work is in relation equal to the total amount of the energy given from the grinding unit 31 (hereinafter simply referred to a grinding energy). The reason why the control is used to increase the force f(t) or to elongate the grinding time t when the above-described clogging occurs is that it is necessary to keep constant the grinding energy. In order to obtain a high quality and stable ground surface without any adverse affect by a change in frictional coefficient, it is ideal to control the grinding energy by the robot 39.